/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2001 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache Lucene" must not be used to endorse or promote products
 *    derived from this software without prior written permission. For
 *    written permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache",
 *    "Apache Lucene", nor may "Apache" appear in their name, without
 *    prior written permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

using System;
using System.Collections.Generic;

namespace DotnetPark.NLucene.Analysis
{
	/// <summary>
	/// Removes stop words from a token stream.
	/// </summary>
	public class StopFilter : TokenFilter 
	{

		private Dictionary<string, string> table;

		///<summary> Constructs a filter which removes words from the input
		///TokenStream that are named in the array of words. </summary>
		public StopFilter(TokenStream ts, string[] stopWords) 
		{
			input = ts;
			table = MakeStopTable(stopWords);
		}

		///<summary> Constructs a filter which removes words from the input
		///TokenStream that are named in the Hashtable. </summary>
		public StopFilter(TokenStream ts, Dictionary<string, string> stopTable) 
		{
			input = ts;
			table = stopTable;
		}
  
		///<summary> Builds a Hashtable from an array of stop words, appropriate for passing
		///into the StopFilter constructor.  This permits this table construction to
		///be cached once when an Analyzer is constructed. </summary>
		public static Dictionary<string, string> MakeStopTable(string[] stopWords) 
		{
			Dictionary<string, string> stopTable = new Dictionary<string, string>();

			foreach(string stopWord in stopWords)
				stopTable[stopWord] = stopWord;

			return stopTable;
		}

		///<summary> Returns the next input Token whose termText() is not a stop word. </summary>
		public override Token Next() 
		{
			// return the first non-stop word found
			for(Token token = input.Next(); token != null; token = input.Next())
			{
				if(!table.ContainsKey(token.TermText))
					return token;
			}
			// reached EOS -- return null
			return null;
		}
	}
}
